Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$201.75	11.804%	$225.5646	$225.56	$225.55	$225.60
Purchase #2	$57.31	8.766%	$62.3338	$62.33	$62.35	$62.30
Purchase #3	$135.95	12.338%	$152.7235	$152.72	$152.70	$152.70
Purchase #4	$75.50	7.805%	$81.3928	$81.39	$81.40	$81.40
Purchase #5	$151.49	13.830%	$172.4411	$172.44	$172.45	$172.40
Purchase #6	$124.62	9.812%	$136.8477	$136.85	$136.85	$136.80
Purchase #7	$86.96	4.181%	$90.5958	$90.60	$90.60	$90.60
7 purchase totals =	$833.58		$921.8993	$921.89	$921.90	$921.80